2003-2012 Polaris Trail Blazer/Boss/Magnum/ATP 330 ATV Engine Piston Ring Kit [Bore Size (mm): 78.45 (Stock)] Bore Size (mm): 78.45 Ring Kits Include Piston Rings Only - Piston Not Included Namura Piston Rings Fit Both Namura and OEM Pistons of the Same Bore Size Unless Otherwise Specified Compatibility: 2003-2012 Polaris Trail Blazer/Boss/Magnum/ATP 330